1. Field of the Invention
This invention relates to a chair, more particularly to a chair, which has a seat supporting unit that can resist left and right tilting of a seat that is supported thereon.
2. Description of the Related Art
Referring to FIGS. 1 and 2, a conventional office chair is shown to include a plastic base plate 11, a soft seat 12, a seat supporting plate 13, two armrest members 14 (only one is visible in FIG. 1), a mobile base 15, and a wooden auxiliary supporting member 16. The seat 12 consists of a solid foam member 121 and a cloth member 122, which is attached to an upper surface of the foam member 121. A backrest member 131 is fixed on a rear portion of the seat supporting plate 13. Each of the armrest members 14 is formed integrally with a horizontal coupling plate 141, which is fixed to the seat supporting plate 13. A casing (not shown) has been proposed to substitute for the expensive solid foam member 121 and the wooden auxiliary supporting member 16, and consists of an upper plate and a lower plate, which are made of plastic and which engage each other along outer peripheries thereof. However, because the plates are made of plastic, which is flexible, they easily deform or even break. For example, when a person sits on the left or right side of the seat 12 or when a person sitting on the seat 12 pushes the armrest arms 14 during the act of standing, the seat 12 tilts to the left or right.